Exile: I will not run from that corpse.
Kreia: There will be another time. Not now, not here, while Korriban runs through himand later on on Malachor V.
Sion: As long as the dark places of this world flow through the cracks of my flesh, I can not be killed.
These quotes clearly show that it is on worlds strong in the dark side that he has this power. As Kreia claims he can be defeaed on Korriban suggesting that at other places he can be, and Sion himself states it is Malachor V's power that allows him to keep himslef alive. Sure he may be able to preform it on other planets, but not as often. Heck, even on Malachor V he is not completlley invincible.
No on has posted ANYTHING that comes anywhere close to overturning thsi post.